This study aimed at testing the effectiveness of an e-module based on ProblemBased Learning combined with Socratic Dialogue on the topic of environmental change in improving school students' critical thinking skills. This research was a quasi-experimental study and used a non-randomised control group, pre-test/posttest design. The sampling technique was cluster random sampling. The sample in this study was two experimental classes (n = 72) and two control classes (n = 72). The data collection instruments included multiple-choice tests and a questionnaire. The test results were analysed using the t-test and the N-gain score test. The results showed significant difference in students' critical thinking skills between the experimental and control classes. Students who used the e-module showed better critical thinking skills. Students who used the e-module showed a greater increase in critical thinking skills after the learning process, compared to students who did not use the e-module. Thus, it can be concluded that the e-module based on PBL combined with Socratic Dialogue effectively improved students' critical thinking skills.